Biological Indicators for Moist Heat, Dry Heat, and Gaseous Modes of Sterilization, Liquid Spore Suspensions
» Liquid spore suspensions may be used to prepare biological indicators for moist heat, dry heat, and gaseous modes of sterilization. On the basis of the intended sterilization use, the suspension is prepared inoculated from a culture of viable spores derived from one of several sterilization resistant microorganisms. Cultures used for liquid spore suspensions include, among others, the following: Clostridium sporogenes, Geobacillus stearothermophilus (formerly B. stearothermophilus), Bacillus atrophaeus (formerly B. subtilis), Bacillus subtilis, or Bacillus coagulans. Each tube or container containing the spore suspension is individually packaged for use. The packaged biological indicator spore suspension has a particular labeled spore count of not less than 103, and not more than 109, spores per mL of suspension. The suspending medium or vehicle is identified according to chemical composition. It has a survival time and kill time appropriate to the labeled spore count, and to the decimal reduction value (the D value, in minutes), specified by the following:
Survival time (in minutes) = not less than (labeled D value) × (log of labeled spore count per mL from 1:100 dilution of original suspension – 2); and
Kill time (in minutes) = not more than (labeled D value) × ( log of labeled spore count per mL from 1 : 100 dilution of original suspension + 4).
Packaging and storage— Preserve in the original tube or container under the conditions recommended on the label, and protect the contents of the tube or container from light, toxic substances, and excessive heat. The materials of composition of the tube or container must not adversely affect the performance of the spore suspension.
Expiration date— The expiration date is determined on the basis of stability studies. The date of manufacture is the date on which the first determination of the total viable count was made.
Labeling— Label the spore suspension tube or container or package insert to state that it is a biological indicator spore suspension for use in label specified applications for moist-heat, dry-heat, and/or gaseous sterilization. State the biological indicator D value obtained under defined exposures to stated sterilization conditions using the Survival Curve Method of D-value analysis. State the Survival time and kill time for the biological indicator suspension under specified conditions on the label. The total viable spore count per mL of the suspension following heat shock treatment must also appear on the label. State in the labeling the strain and ATCC number of the microorganisms used in the spore suspension and instructions for spore recovery and for safe disposal of the suspension. Indicate in the labeling that the stated D value is reproducible only under the exact conditions determined by the manufacturer and that the user would not necessarily obtain the same results if different exposure conditions were used. State that the user should determine the suitability of the biological indicator spore suspension for the user's particular purpose and exposure conditions.
Identification— Identification for the biological indicator is of lesser importance than the more relevant concerns of population and resistance to the sterilization processes. The manufacturer should identify the species used.
D value— If the biological indicators are being used in moist-heat or dry-heat sterilization, proceed as directed for the relevant procedure in the section D-Value Determination under Biological Indicators—Resistance Performance Tests 55. The requirements of the test are met if the determined D value is within 20% of the labeled D value for the selected sterilizing conditions, and if the confidence limits of the estimate are within 10% of the determined D value. The D-value determination method used should be that identified by the biological indicator manufacturer.
Survival time and kill time— Follow the procedure under Survival Time and Kill Time in the section D-Value Determination under Biological Indicators—Resistance Performance Tests 55. The test is conducted using 1:100 dilution aliquots of the original suspension to inoculate carrier substrates that are most likely to be used by the purchaser of the spore suspensions for a given mode of sterilization. Following a total viable count analysis, the inoculated substrates are subjected to sterilization exposure conditions intended to indicate survival. The inoculated carriers must show evidence of growth among the exposed carriers. A second study is conducted to demonstrate the conditions necessary to result in total kill of the carriers. None of the carriers subjected to conditions designed to induce total kill should show growth. If for either the survival-time test or the kill-time test, not more than one carrier out of both groups fails the survival or kill requirements, continue the corresponding test with four additional groups, each consisting of 10 carriers, according to the procedure described. For biological indicators for use with moist-heat or dry-heat sterilization, if all of the additional specimens subjected to the specific sterilization process either meet the survival requirements for the survival-time test or meet the kill requirement for the kill-time test, whichever is applicable, the requirements are met.
Total viable spore count— Proceed as directed for Biological Indicators for Moist Heat, Dry Heat, and Gaseous Modes of Sterilization, Liquid Spore Suspensions in the section Total Viable Spore Count under Biological Indicators—Resistance Performance Tests 55. The requirements for this test are met if the total viable spore count within the suspension is within ±1 log of the value stipulated by the manufacturer.
Purity— There is no evidence of contamination with other microorganisms following examination of spores recovered from the metal carriers using suitable plate-culture medium.
Shipment— Spore suspensions must be shipped following EPA requirements for the shipment of biological and/or etiological agents.
Disposal— Spore suspensions that a user or manufacturer wishes to dispose of are first sterilized by moist heat by a process that achieves temperatures of approximately 121 for not less than 30 minutes. Alternative sterilization methods yielding equivalent or greater levels of lethality may be used.
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Topic/Question Contact Expert Committee
Monograph Radhakrishna S Tirumalai, Ph.D.
Principal Scientific Liaison
(GCM2010) General Chapters - Microbiology
USP35–NF30 Page 2358
Pharmacopeial Forum: Volume No. 30(1) Page 66